Abstract

Question

Data sources

Studies were identified by searching MEDLINE, EMBASE/Excerpta Medica, BIOSIS, AMED
(British Library), CISCOM (Research Council for Complementary Medicine, London), and
the Cochrane Library (to June 1998); scanning bibliographies of relevant articles
and personal files; and contacting experts and the leading manufacturers of kava extract.

Study selection

Studies in any language were selected if they were randomized, double-blind, controlled
trials (RCTs) that compared single preparations of kava extract with placebo. Names
of authors, institutions, and journals and addresses were removed before selection.

Data extraction

2 reviewers independently assessed the quality of study methods by using the Jadad
scale (maximum score of 5), and they extracted data on setting, study design, patient
characteristics, kava extract regimen, Hamilton Rating Scale for Anxiety (HAM-A) scores,
and adverse effects. Standardized, predefined criteria were used to extract data,
and disagreements were resolved by discussion.

Main results

7 RCTs (377 patients) met the selection criteria. 6 RCTs had quality scores ≥ 3.
The results of 3 RCTs (198 patients) that used a common outcome measure (HAM-A total
score) were combined in a meta-analysis. The same kava extract dose was used in all
3 RCTs: kava extract WS1490, 100 mg 3 times daily for 4, 8, or 24 weeks. Kava extract
led to a greater reduction in HAM-A total score from baseline than did placebo (weighted
mean difference 9.69, 95% CI 3.54 to 15.83). The 4 studies that could not be combined
in the meta-analysis reported a greater reduction in anxiety for kava extract than
for placebo. 5 RCTs reported adverse effects in patients who received kava extract:
stomach complaints, restlessness, drowsiness, tremor, headache, and tiredness.

Commentary

Anxiety symptoms and disorders are common in primary care and hospital services, but
they often go unnoticed. They are disabling and frequently associated with depression
and substance abuse. Conventional treatment is with antidepressants or benzodiazepines,
but this therapy is usually only partially successful, with adverse effects described
by many patients (1).

The meta-analysis by Pittler and Ernst suggests that kava extract may be a useful
addition to the therapeutic options. The main result is derived from 3 relatively
small trials, which is similar to the evidence base for antidepressants in anxiety
(1). Most of the trials have been done in Germany; studies in other countries are both
warranted and necessary. A mean reduction of 9 points on the HAM-A for the comparison
of kava extract with placebo is likely to represent a clinically significant benefit,
although the presentation of results does not allow direct comparison with other interventions
for anxiety.

Some doctors may be skeptical that an herbal extract could be as effective as a synthetic
drug. From that perspective, it is worth noting that some adverse effects were reported
in 2% to 12% of the patients in the trials reviewed by Pittler and Ernst. Skepticism
is fine if we are similarly wary for all new interventions and avoid double standards.
Equally, we must guard against unbridled enthusiasm for a “natural” remedy. It is
possible that some persons with anxiety will try kava extract before consulting their
doctor. If they are started on other medications, the potential exists for substantial
drug interaction, as has been seen with St. John’s wort in the treatment of depression.

Physicians have a new treatment option for anxiety, but they will need to avoid polytherapy
and carefully monitor for possible drug interactions.